There are many circumstances in which materials in the form of a fine powder are conveniently stored and transported in sacks. Relatively large quantities of powder material are frequently contained in what are commonly known in the industry as "supersacks" which are typically made of a strong tightly-woven fabric and are provided with an end opening closeable by a drawstring. Such a supersack may have loops, rings, or other elements attached conveniently at an end opposite to the openable end for suspension, hooking, or other conventional attachment of the sack with the opening disposed to discharge the contents downwardly.
The fabric of the supersack being finely woven has the quality that the powder material contained therein cannot leak out in normal handling of the sack. However, molecules of gases contained in the ambient atmosphere, being much smaller than the average size of a particle of the powder material, can leak into the sack as powder material is extracted from within. This ensures against undesirable particulate pollution of the ambient atmosphere in routine handling of a closed sack. However, when the sack is opened to extract powder material therefrom, there is always a substantial likelihood that some of the powder material will escape into the atmosphere. One solution is to enclose the sack, and particularly the opening from which the part of the material flows, to minimize such pollution. Augers are often used to promote the outflow of powder material between containers or from a container to apparatus for forming a slurry.
U.S. Pat. No. 5,161,887, to Goldberg et al., titled "Process for Producing an Aqueous Solution of Difficult-to-dissolve, Fine Particle Size Particulate Material", teaches a system in which a fine particulate material is contained in a large sealed bag which includes a tube that unfolds and extends from beneath a lower portion of the sack. This tube fits into a hopper adapter and a cord is thereafter untied to allow the particulate material to flow outward. This outflow is controlled and assisted by an auger feeder, which delivers it into a mixing vessel where it is mixed with a stream of water. A partial vacuum is applied to the mixed flow which is passed through a high speed mixing pump to obtain the desired solution.
U.S. Pat. No. 4,955,723, to Schneider, titled "Slurry Mixing Apparatus with Dry Powder Conveyer", teaches a system in which a vacuum generated by a vacuum pump is applied to a flexible conduit dipped into an open sack of powdered material to entrain the material with air sucked via the conduit. The sucked-up material is directed to fall onto an upper surface of a quantity of liquid contained and stirred in a closed tank to cause mixing thereof to form a slurry.
U.S. Pat. No. 4,778,280, to Brazelton, titled "Mixing Apparatus", teaches an apparatus in which dry particulate material is fed through a funnel into a casing which receives water circumferentially so as to create a swirl.
U.S. Pat. No. 4,007,921, to Zingg, titled "Apparatus for Mixing Dry Particles with a Liquid", teaches an apparatus in which dry cement particles fall downward through a hopper, past a regulating valve into a mixing compartment to be mixed with a water flow. The resulting mixture is flowed into a rotating impeller which recirculates a portion of the resultant slurry. Thus, as some slurry is drawn away from the system, the rest recirculates and is intensely mixed with an added supply of water mixed with cement particles.
The above-discussed exemplary prior art requires relatively complex apparatus which is expensive to install and maintain, does not ensure against particulate air pollution, and can experience problems related to clogging of the particulate outflow from the original container or sack.
Accordingly, there is a perceived need for apparatus and a method for transferring powder material from a conventional large sack and for efficiently mixing it at a controlled rate into a liquid to form a slurry while ensuring against atmospheric pollution due to leakage of the powder material into the atmosphere. The present invention, as described and claimed below, is intended to provide a simple, efficient, and affordable solution to this need.